Device for laying a plastic film on a roller

ABSTRACT

A device for laying a plastic film on a roller (7), especially a molten plastic film on a drying roller (7), with an air squeegee (15) having an air outlet aperture (25) extending transversely above the foil web (1), is integrated into the air squeegee (15) for edge blowing and is arranged in such a way that a common shared effective pressure application line is produced, and/or the air outlet apertures (27) of the air squeegee (15) can be adjusted along said air squeegee (15) and thus to differing effective widths across the foil web.

BACKGROUND OF THE INVENTION

The invention relates to an apparatus for laying a plastic film on aroll, in particular for laying a polymer melt film on a chill roll.

In the production of plastic films, it is basically usual to press themelt film emerging from a slot dye onto a chill roll by means of aso-called air knife, whilst producing an adequate air velocity (dynamicpressure). In this case, the air knife extends in its longitudinaldirection transversely over the width of the melt film, that is to saytransversely to the take-off direction of the plastic film, air beingable to emerge in the direction of the melt film via a continuous exitslot, generating a corresponding air velocity.

Since the melt film has a thicker edge, this must be pressed onto thechill roll with greater force. As a result, it is also necessary topursue the objective of minimizing an inward step in the width of thefilm, that is to say to ensure that the width of the melt film remainsas constant as possible during the plastic film production.

An apparatus forming the generic type has been disclosed by U.S. Pat.No. 4,255,365. The air knife disclosed by this apparatus has amultiplicity of air exit openings that are arranged in an offset mannerin the longitudinal direction of the air knife and are directed onto thefilm web. This opens the possibility of producing different contactpressures over the length of the air knife, that is to say over thewidth of the plastic film web, in order ultimately to influence thethickness profile of the film.

However, in the case of this previously known apparatus, it is alsonecessary to use so-called "edge pipes" at the two edges of the film, inorder to generate here in a deliberate way the higher contact pressureforces that are needed, matched to the respective film width. Finally, adesign of this type is also only suitable for a specific width of aplastic film web.

It is therefore the object of the present invention to overcome thedisadvantages according to the prior art, and to provide an apparatusimproved in this regard for laying a plastic film on a roll, inparticular for laying a polymer melt film on a chill roll.

SUMMARY OF THE INVENTION

According to the invention, it has been shown that, in particular in thecase of higher take-off speeds, an offset, present in the take-offdirection, of the effect lines of the exit openings of the air knife andof the means separately provided for blowing on the edge isdisadvantageous. Such an offset of the effect lines of the means forblowing on the edge and of the blowing by the air knife has severaldisadvantages. It leads not only to distortion of the film, but alsooften causes markings on the film, especially in the edge region. As aresult of the offset the effect lines in the prior art, it is oftenpossible to detect blowing-in of the pressure air in the edge regionbetween the roll and the film, as a result of which film edges that donot run quietly are produced, and the undesired turning up of the edgesis possibly also favored. Finally, it is also possible to determine amutual negative influence when adjusting the air knife and/or the meansfor blowing on the edge.

By contrast, according to the invention a joint, straight effect andlaying line over the entire width of the film web, including the meansfor blowing on the edge, is made possible. As a result of this optimal,joint laying effect line, the risk present in the prior art of theoccurrence of transverse markings on the film is reduced, and the riskof blowing in waste air in the edge region between roll and film isreduced. This also allows the most constant flat film edges to beachieved.

As an alternative, or in addition, provision is further made for the airknife to be adjustable in its longitudinal direction, that is to saywith its effective width extending transversely to the plastic film web,that is to say in particular from the point of view of its effective airexit openings. This allows the laying-on width to be matched simply andprecisely to the film width in an optimum way, in order in particularalso by this means to avoid the lateral blowing in of air between rolland film, as a result of which the disadvantages mentioned above areeliminated. In this case, the slot width of the air exit opening in theair knife remains unchanged.

What has proven to be particularly advantageous is the width adjustment,performed transversely to the take-off direction, of the air knife inorder to match it to the plastic film width given the presence of thedevice, integrated into the air knife, for blowing laterally on theedge, since as a result it is possible to realize a joint andsimultaneous adjustment of the width of the blowing slot and hence theadaptation of the position of the means for blowing on the edge. Inparticular, it is possible to ensure by this means that the lateralblowing in of air between roll and film is reliably avoided.

In a development of the invention, provision is made for the device forblowing on the edge to be either implemented completely separately fromthe air-knife blowing, to be adjustable and hence controllable, or elsefor provision to be made for a smooth transition between the airstreams, which are directed toward the foil, on the one hand in theregion, that is to say in the central region, of the air knife and, onthe other hand, in the edge regions for blowing on the edge.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURES

The invention is explained below using drawings of different exemplaryembodiments. Here, in detail:

FIG. 1: shows a schematic side view of the apparatus according to theinvention;

FIG. 2: shows a schematic cross-sectional illustration through the airknife according to the invention;

FIG. 3: shows a perspective illustration of the one adjustable air-knifeelement;

FIG. 4: shows a schematic vertical sectional illustration of an extractin the longitudinal direction of the air knife, in the region of itschamber for blowing on the edge;

FIG. 5: shows a cross-sectional illustration along the line V--V in FIG.4;

FIG. 6: shows a modification of FIG. 4; and

FIG. 7: shows a further exemplary embodiment modified in relation toFIG. 3.

DESCRIPTION OF A PREFERRED EMBODIMENT

Illustrated in a schematic side view in FIG. 1 is a plastic film 1, inparticular a polymer melt film 1, such as is laid, following thedirection of the arrow 3, by a slot die onto a surface 5 (a section ofwhich is shown in an axial front side view) of a roll 7, which is alsoreferred to below as a chill roll.

In order to generate the necessary contact forces for laying the polymermelt film 1 onto the chill roll 7, an apparatus 9, which is intended tolay the polymer melt film on the chill roll and extends over the widthof the polymer melt film 1, that is to say transversely to the take-offdirection of the plastic film, is illustrated.

In its left-hand part illustrated in FIG. 1, this apparatus comprises anair distribution chamber 11, which is used for uniform air distribution.Adjoining this, via one or more connecting ducts 13, is a so-called airknife 15, which is explained in more detail using the followingschematic drawing. In this case, the air knife extends in itslongitudinal direction transversely to the plastic film 1, that is tosay transversely to the take-off direction of the plastic film 1. Tothis extent, the effective width of the air-knife 15 is also spoken ofbelow, that is to say the effective width related to the width of theplastic film.

According to the schematic cross-sectional illustration of FIG. 2, theair knife 15 essentially comprises two air-knife elements 15a and 15b.These air-knife elements 15a and 15b are of identical construction, atleast in cross section, and essentially have an L-shaped configurationin the cross-sectional illustration according to FIG. 2. The twoair-knife elements 15a and 15b are in this case arranged rotated through180° with respect to each other, with the result that in each case thefront wall 17 of the comparatively narrow-configuration short limb 19 ofthe inlet sic! air knife 15 rests on the supporting wall 21, runningtransversely to the plastic film web 1, of the long limb 23 of therespective other air knife 15. This forms a chamber 25 that is closed inthe circumferential direction and through which the air can flow atright angles to the plane of the drawing.

This results in a lower slot-shaped air exit opening 27.

Formed in each case on the air-knife element 15a and 15b, on which therelevant short limb 19 is also formed, are webs 29, which arewedge-shaped in the cross-sectional illustration and in each case arelocated offset inward toward the boundary wall of the shorter limb 19.

This arrangement results in a central chamber 31 that is essentiallyadjustable at least virtually over the entire width of the plastic filmweb 1, and outer chambers 33 for blowing on the edge, which are in eachcase located on the outside and separated from said central chamber 31by the webs 29.

As emerges from the schematic perspective illustration according to FIG.3, compressed air coming from the air distribution chamber 11 (FIG. 1)and also referred to below as blower air 35, can be fed from the rearside of the air knife 15 to the central chamber 31, this blower air 35,following the arrow 37 illustrated in FIG. 3, flowing out in thedirection of the film via the central chamber 31, virtually over theentire width of the polymer melt film 1, via the lower air exit opening27.

It can also be seen from FIG. 3 that the outer chambers 33 may possiblyno longer be separated or offset from the central chamber 31 via saidweb 29, but also via a rear wall 39, so that high-pressure or compressedair 41 at higher pressure than the blower air 35 can be discharged via aseparate feed duct 43, separately from the blower air, downward via therespective lateral feed duct 43 and the respective outer chamber 33, anddownward via the lateral air exit openings 27', in accordance with thearrow illustration 42.

Since the two air-knife elements 15a, 15b, which are also referred to inpart below as air-knife lips, can be displaced relative to one anotherin the longitudinal direction (that is to say transversely to thepolymer melt film web 1) in accordance with the arrow illustration 44 inFIG. 2, the effective length of the central chamber 31 can be changedthereby. In spite of this displaceable arrangement of the air-knife lips15a, 15b, the width for the means for blowing on the edge is keptconstant, since the length of the outer chamber 33 remains unchanged. Asa result of this arrangement, an optimum adaptation to the effectivewidth of the polymer melt film width can be undertaken simply, a joint,straight contact and effect line for pressing the melt film 1 on thechill roll 7 always being produced. In this case, the pressure forproducing higher contact forces at the edge of the melt film can beadjusted to an appropriate, desired level that is different from thepressure of the blower air, as a result of the separate feeding ofcompressed air.

It can also be seen from the illustration according to FIGS. 3 and 4that the webs 29 can also be arranged and shaped in such a way that nocomplete separation is effected between the central chamber 31 and theouter chambers 33. The effect of the design variant according to FIGS. 3and 4 is that the compressed air 41 fed via the outer chambers 33, andthe blower air 35 fed via the central chamber 31, mix before reachingthe air exit gap 27 and 27' into the environment, which is located atthe bottom, in order to achieve a smooth transition of the contactforces.

To this end, the webs 29 according to FIGS. 3 and 4 are not configuredto run in a wedge shape in a cross-sectional plane parallel to theplastic film web (that is to say parallel to the lower air exit gap 27),but end alternatively in addition already above the plane of the airexit opening 27. In this case, according to the sectional illustrationin FIG. 5, the front edge 45 of the web 29 is chamfered, with the resultthat, depending on the geometry selected, increasing mixing betweencompressed air and blower air takes place, the closer the two streamscome to the air exit opening 27, 27'.

In order optionally to implement different outflow geometries, inparticular also from the point of view of simple adaptation to differentraw materials used, film thicknesses, plant speeds and/or otherparameters, etc., provision can further be made that, in the outerchambers 33 or in the chamber formed as a whole by the air-knifeelements 15a, 15b, it is possible to use different inserts, located onthe outside, also compressed-air chamber inserts 33' below. The webs 29thus become part of a replaceable insert, in order here to be able toundertake simple adaptation to different desired geometries.

The separation or displacement plane E between the two air-knifeelements 15a and 15b in the schematic illustration of FIGS. 2 and 3 can,for example, be formed along the dashed line A--A or, for example, alsoB--B or C--C in FIG. 1 or another suitable point.

Using FIG. 6, and deviating from FIG. 4, it is only indicated that thegeometry of the outer or high-pressure chamber 33 and/or of the web wall29 can also be selected differently in adaptation to different plasticfilms, parameters, etc. for the purpose of optimization. In the case ofthe exemplary embodiment according to FIG. 6, the side walls areconfigured with an outwardly directed component in the flow direction.This can make it possible for the emerging high-pressure air to emergefrom the air gap 27' not only with a flow component perpendicular to theplane of the plastic film, but also with an outwardly directed componentpointing away from the plastic film central longitudinal line. The angleof inclination to the film web may be, for example, 0° to 45°, inparticular 15° to 20°. Here, the replaceable inserts mentioned prove tobe particularly beneficial, since in this way inserts with differentgeometries can be used at any time without problems.

Finally, using FIG. 7, it is merely indicated that, deviating from FIG.2, the webs 29 are not arranged on the air-knife element 15a or 15b thatis provided with the short limb 19, and hence moveable therewith, but onthe respectively opposite air-knife element 15a or 15b. An adjustment inthe longitudinal direction of the air knife and hence in the widthaction, related to the plastic film web, results from the fact that notonly the effective length in the effective width of the central blowerair chamber 25, but also the length in the effective width of the outerchambers 33, are differently adjustable.

I claim:
 1. Apparatus for laying a polymer melt film web on a chillroll, comprising:an air knife extending in its longitudinal directiontransversely across the film web and transverse to a take-off directionfor the film width, said air knife including one or more first air exitopenings for flowing air under pressure toward the plastic film web in adirection having a flow component transverse to the film web, said airknife carrying discrete devices for flowing air through second exitopenings onto opposite transverse edges of the plastic film web with airpressure and/or air velocity elevated with respect to the air pressureand/or velocity of the air flowing from said first exit openings, saiddevices forming an integral part of said air knife, said air knife beingadjustable such that said first air exit openings are adjustable toprovide different effective widths in the longitudinal direction of theair knife transversely to the take-off direction of the film web. 2.Apparatus according to claim 1 wherein the size of said second air exitopenings remains unchanged when the length of said first air exitopenings of the air knife is adjusted.
 3. Apparatus according to claim 1wherein said air knife comprises a central chamber for flowing air ontothe middle of the plastic film through said first exit openings and atleast two outer chambers on opposite sides of said central chamber forflowing air onto edges of the plastic film through said second exitopenings.
 4. Apparatus according to claim 1 wherein said air knifecomprises at least two air knife elements each having a length dimensionand a substantially L-shaped cross-section transverse to the air flowdirection, said elements being juxtaposed with said L-shapedcross-sections in opposition to one another to define a closed airpassage chamber between and generally parallel to the lengths of saidL-shaped elements, the length of said chamber being adjustable byrelative displacement of the two air knife elements in a directiongenerally parallel to their lengths.
 5. Apparatus according to claim 3wherein said outer chambers are each separated from said central chamberby a wall.
 6. Apparatus according to claim 5 including a discretehigh-pressure feed duct for supplying high-pressure air to said outerchambers at a pressure higher than the pressure of air supplied saidcentral chamber.
 7. Apparatus according to claim 5 wherein said wallsare shaped to provide complete separation of the outer chambers from thecentral chamber.
 8. Apparatus according to claim 5 wherein said wallsare shaped to provide only partial separation between the outer chambersand the central chamber such that air introduced into the outer chambersat least partially mixes with at least part of the air introduced intothe central chamber before flowing through the first and second air exitopenings.
 9. Apparatus according to claim 5 wherein said walls arealigned at an angle such that air flowing through said first exitopenings of the outer chambers in the direction of the film web emergeswith a flow component directed obliquely onto the plastic film edge andwithin a range of 0° to 45°.
 10. Apparatus according to claim 9 whereinsaid outer chambers are shaped such that air flowing through said secondopenings flows with a flow component directed toward the film edge at anangle of 15° to 20°.
 11. Apparatus according to claim 5 wherein saidwalls have a decreasing wall thickness in the direction of the air exitopenings.
 12. Apparatus according to claim 5 wherein the outer chambersincluding said walls comprise replaceable inserts.
 13. Apparatusaccording to claim 1 wherein said air knife comprises a central chamberfor flowing air onto the middle of the plastic film through said firstexit openings and at least two outer chambers on opposite sides of saidcentral chamber for flowing air onto edges of the plastic film throughsaid second exit openings, said air knife comprising at least two airknife elements each having a length dimension and a substantiallyL-shaped cross-section transverse to the air flow direction, saidelements being juxtaposed with said L-shaped cross-sections inopposition to one another to define said central chamber between andgenerally parallel to the lengths of said L-shaped elements, the lengthof said chamber being adjustable by relative displacement of the two airknife elements in a direction generally parallel to their lengths, saidwalls being arranged on the air knife elements forming said outerchambers.
 14. Apparatus according to claim 1 wherein said air knifecomprises a central chamber for flowing air onto the middle of theplastic film through said first exit openings and at least two outerchambers on opposite sides of said central chamber for flowing air ontoedges of the plastic film through said second exit openings, said airknife comprising at least two air knife elements each having a lengthdimension and a substantially L-shaped cross-section transverse to theair flow direction, said elements being juxtaposed with said L-shapedcross-sections in opposition to one another to define said centralchamber between and generally parallel to the lengths of said L-shapedelements, the length of said central chamber being adjustable byrelative displacement of the two air knife elements in a directiongenerally parallel to their lengths, said outer chambers beingadjustable in length in the longitudinal direction of the air knife byrelative displacement of the two air knife elements and having outerboundary walls formed on respective air knife elements, and websdelimiting the outer chambers from the central chamber being seated onrespective opposite air knife elements.